In the field of products concerning the optical disk such as CD, DVD and the like, there is a tendency to increase both the storage capacity, and the speed of data transfer in order to be competitive and capture market share. Also, with the capacity of the optical disk increased, marks and spaces (corresponding to a representation of the 1s and 0s of information) to be formed on the optical disk are smaller and more precise, and the formation of such fine marks and spaces is required to be more flexible and accurate in the optical disk apparatus.
Factors such as media type, writing speed, disc format and drive optics necessitate particular write strategies, which are used to write the marks and spaces. In general, the writing of marks on a disk can be considered to compose of the first pulse which defines the starting edge of a mark, multipulses which fill the center of a mark, and the last pulse which defines the ending edge of a mark. A key portion of the write strategy is the definition of multipulse locations and timing in response to NRZ input data (or NRZI input data).
Previous write strategy generators were very limited with regards to how multipulses can be defined. For example, for CD and DVD, the minimum mark length is 3 T, and longer marks are 4 T, 5 T, 6 T, etc, up to 14 T. A 3 T mark would be formed with a single pulse which would define both the leading and tailing edges of the 3 T mark. The reason only one pulse would be used is that the laser spot size is comparable to the size of the 3 T mark itself. A 4 T mark would typically be defined by either one large pulse, or two small pulses. A 5 T mark would be defined either by two or 3 pulses. If it was composed of three pulses, the center pulse would be a multipulse. A 6 T mark would be composed of 3 or 4 pulses, with either 1 or 2 multipulses. A key restriction of early write strategies is that one and only one multipulse strategy could be programmed for each mark length. Thus they were called “1 T multipulse strategies”. However, as optical drives increased in speed, the media was not fast enough to respond to a 1 T multipulse strategy, nor was there enough time to bring the drive currents up and down in the low nanosecond intervals required to implement the 1 T multipulse strategy. Accordingly, a “2 T multipulse strategy” began to be used, where a multipulse is placed every other T between a first and last pulse of a mark, with the multipulse pattern optionally being different for even mark-lengths than for odd mark-lengths. However, other “custom” multipulse strategies are sometimes desired, potentially requiring that custom chips be designed, which is typically not cost effective. Accordingly, given the variety of existing and prospective write strategies in the market, it is desirable to provide for greater flexibility in defining multipulses. From a design point of view, efficiency and compactness of the implementation are important considerations.
Other key portions of a write strategy include definitions of the first pulse and last pulse in response to NRZ input data, as well as the modulation code that is used. The modulation code for CD and DVD used EFM, or enhanced EFM, both of which have marks of 3 T, 4 T, etc. But Blue recording media has a modified 17PP code which has marks of 2 T, 3 T, 4 T, etc. As mentioned earlier, there is also desire for some flexibility in choosing when and how many multipulses to fit within a given mark as well.
In addition to this, there is an issue that has to do with the influence of size of the spaces surrounding a mark to the strategy itself. For instance, if a mark is preceded by a 3 T space, the optical and thermal history before the first pulse would dictate that the position of the first pulse be changed depending on both the size of the mark, and the size of the preceding space. Likewise, the timing of the last pulse would be influenced by the size of the mark and the following space. This led to a array of programmable pulse start and duration times for the first and last pulses. Ideally, the array would cover all mark and space sizes from 2 T through 14 T. But in practice, this requires excessive programming space and time. So the array is typically shortened to a 4×4 array that includes 3 Tm, 4 Tm, 5 Tm, 6 Tm, and the corresponding 3 Ts, 3 Ts, 4 Ts, and 5 Ts, where Tm means length of a mark in T's, and Ts means length of a space in T's. However, this 4×4 array was not always desired by a customer, which may result in a custom chip being designed. Accordingly, it would be useful if the array arrangement were more flexible, thereby not requiring a new design each time a customer wanted to redefine the array.
Typically, a write strategy generator will only offer one or two combinations of such modulation codes and timing modes, as well as only one way of organizing data that defines parameters such as the first and last pulse of a mark. Again, greater flexibility in selecting combinations of modulation codes and timing modes, as well as in organizing the data that defines write strategy parameters (such as first and last pulse of a mark) is desirable, to thereby reduce the need for custom chips. From a design point of view, efficiency and compactness of the implementation are again important considerations.